As explained in Chapter 16.2 ("Gear Hobbing") of Dudley's Gear Handbook, Second Edition, McGraw-Hill, Inc., New York, N.Y. (1992) at pages 16.6 et seq., almost any external tooth form that is spaced uniformly about a center can be hobbed. Usually, in generation of a gear tooth by a hobbing process, a cutting tool and a workpiece rotate in a constant relationship between their rotational speeds while the cutting tool is fed into the workpiece. The cutting tool, which is known as a hob, is a fluted worm having radially relieved teeth arranged in a helical pattern.
Heretofore, specialized hobbing machines have been employed, which tend to be very expensive. Generally, a hobbing machine of an older type employs a gear train with changeable gears to maintain the constant relationship between the rotational speeds of the hob and the workpiece, whereas a hobbing machine of a newer type employs computer numerical control (CNC) and a so-called electronic gear box (EGB) to maintain the constant relationship therebetween.
Many machine shops have vertical milling machines of a type comprising a column, a knee mounted to the column so as to be vertically positionable with respect to the column, a saddle mounted to the knee so as to be horizontally positionable with respect to the knee, toward and away from the column, a table mounted to the saddle so as to be horizontally positionable with respect to the saddle, in opposite directions across the column, a head projecting from the column, an arbor mounted operatively to the head and rotatable about a generally vertical axis, and a motor for rotating the arbor about the generally vertical axis. Vertical milling machines of this type are available from various manufacturers including Bridgeport Machines of Bridgeport, Conn.
In many machine shops, it would be very useful if a vertical milling machine of the type noted above could be somehow adapted to perform the hobbing process.